Cultivation greenhouses prevent vegetables within the greenhouses from being directly influenced by external air, which enables controlling environments other than sunlight, such as temperature, humidity, air flows and watering, thereby stabilizing production and product quality, in comparison with outdoor cultivations which are directly influenced by atmospheric temperature and weather. Cultivation greenhouses of sunlight-use types which utilize only sunlight and cultivation greenhouses of sunlight-parallel-use types which partially utilize photonic synthesis through sunlight are popular, since they enable cultivations in season-shift manners and sales with higher prices, in comparison with complete-control type plant factories which perform photonic synthesis only through artificial light sources without utilizing sunlight. Cultivation greenhouses generally include plastic greenhouses and glass greenhouses and have been installed in various areas, as well as in cold areas in Japan, at the present time.
A plastic greenhouse includes iron pipes or wooden members as its frames and also is covered at its outer walls with synthetic resin films made of polyethylene, polyvinyl chloride or the like. Plastic greenhouses are reduced in transmittance, since the resin films therein are degraded by ultraviolet rays in sunlight, which necessitate replacement of these films at regular time intervals. However, these plastic greenhouses are more inexpensive than glass greenhouses provided with large-sized and heavy glass plates and are used in wider ranges than those of glass greenhouses. Plastic greenhouses necessitate replacement of resin films at regular time intervals and, furthermore, have the problem of the occurrence of damages of crops therein and collapse of the greenhouses themselves in the event that the vinyl films are fractured by strong winds. This problem is also induced in glass greenhouses more than a little.
As a countermeasure against collapse of vinyl greenhouses, in JP-A No. 9-51729, beams are formed from iron pipes with larger thicknesses, similarly to the supporting columns, and nets or vinyl sheets integrated with tension-construction wires are mounted to the outer sides of greenhouses. In JP-A No. 2001-95397, films or nets which are attached to greenhouses are enabled to be completely eliminated or upwardly wound immediately before the occurrence of typhoons, further two films are provided and stretched such that they overlap with each other, arch pipes arranged in conformance to a ridge are bound to one another at their center portions through reinforcing ropes, and these ropes are coupled, at their opposite ends, to a vertical frame pipe. In JP-A No. 2002-78421, poles are erected outside outer-peripheral poles constituting a greenhouse framework with intervals provided therebetween, pipes are coupled to both the poles therebetween for reinforcing them with each other, and this framework is placed at a predetermined interval from the greenhouse in the circumferential direction and is coupled to the greenhouse.
Prior Art Literature
Patent Literature
Patent Literature 1: JP-A No. 9-51729
Patent Literature 2: JP-A No. 2001-95397
Patent Literature 3: JP-A No. 2002-78421
Non-Patent Literature
Non-Patent Literature 1: Masaki Takatsuji, “The Basic and Practices of Plant Factories”, Shoka Shobo